Endoscope system having a first light source for imaging a subject at different depths and a second light source having a wide band visible band

ABSTRACT

An endoscope system of the present invention includes: a first illumination unit that emits first illumination light for imaging two sets of image information about a subject at different depths; a second illumination unit that emits second illumination light having a wide band covering a visible band from a position different from the position of the first illumination light; an imaging unit that images a first illumination image and a second illumination image of the subject that is illuminated with the first illumination light and the second illumination light; a separation processing unit that separates the two sets of image information from the first illumination image; and a separated-image generating unit that generates two separated images by processing the second illumination image using the two sets of image information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of International Application PCT/JP2017/021664,with an international filing date of Jun. 12, 2017, which is herebyincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to endoscope systems.

BACKGROUND ART

Light produced by an illuminated object contains a plurality of types ofcomponents, such as specular reflection light, diffuse reflection light,and scattered light. A proposed technique separates these componentscontained in an object image using a high-frequency pattern projectionmethod, which uses structured illumination light having a stripelight/dark pattern, to separate information about the surface of theobject and information about the inside of the object (for example, seeNon-Patent Literature 1).

A technique for measuring the shape of an object also uses structuredillumination light (for example, see Patent Literatures 1 and 2).Structured illumination light is generated by utilizing interference oflight in Patent Literature 1, and structured illumination light isgenerated by projecting a grid pattern formed on a substrate in PatentLiterature 2.

CITATION LIST Non-Patent Literature

{Non-Patent Literature 1} Tsuyoshi TAKATANI et al., “Decomposition ofReflected and Scattered Lights by Multiple Weighted Measurements”, The14th Meeting on Image Recognition and Understanding (MIRU2011), July,2011

Patent Literature

{PTL 1} Japanese Unexamined Patent Application Publication No.2016-200418

{PTL 2} Japanese Unexamined Patent Application Publication No.2016-198304

SUMMARY OF INVENTION

An aspect of the present invention is an endoscope system including: afirst illumination unit that emits, from a first exit face to a subject,first illumination light for imaging two sets of image information aboutthe subject at different depths; a second illumination unit that emits,from a second exit face disposed at a different position from the firstexit face to the subject, second illumination light having a wide bandcovering a visible band; an imaging unit that images a firstillumination image of the subject illuminated with the firstillumination light, and a second illumination image of the subjectilluminated with the second illumination light; a separation processingunit that separates the two sets of image information from the firstillumination image; and a separated-image generating unit that processesthe second illumination image using the two sets of image information togenerate two separated images each containing a large amount ofinformation about the subject at the different depths.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the overall configuration of an endoscope system accordingto an embodiment of the present invention.

FIG. 2A shows an example intensity distribution of first illuminationlight and the temporal change thereof.

FIG. 2B shows another example intensity distribution of the firstillumination light and the temporal change thereof.

FIG. 2C shows another example intensity distribution of the firstillumination light and the temporal change thereof.

FIG. 2D shows another example intensity distribution of the firstillumination light and the temporal change thereof.

FIG. 2E shows another example intensity distribution of the firstillumination light and the temporal change thereof.

FIG. 2F shows another example intensity distribution of the firstillumination light and the temporal change thereof.

FIG. 3A shows an example spatial profile of the intensity of the firstillumination light.

FIG. 3B shows another example spatial profile of the intensity of thefirst illumination light.

FIG. 3C shows another example spatial profile of the intensity of thefirst illumination light.

FIG. 3D shows another example spatial profile of the intensity of thefirst illumination light.

FIG. 3E shows another example spatial profile of the intensity of thefirst illumination light.

FIG. 3F shows another example spatial profile of the intensity of thefirst illumination light.

FIG. 4 is a diagram showing processing for generating a surface-layercomponent image and a deep-layer component image in a separationprocessing unit.

FIG. 5 is a diagram showing the relationship between: specularreflection light, surface scattered light, and internal scattered lightproduced in biological tissue by being irradiated with the firstillumination light; and the positions where these types of light areproduced.

FIG. 6 is a diagram showing a method for generating the surface-layercomponent image and the deep-layer component image in the separationprocessing unit.

FIG. 7 is a diagram showing processing for generating the surface-layerimage and the deep-layer image in a separated-image generating unit.

FIG. 8 is a diagram showing a method for calculating intensity valuesImax and Imin by using a phase shift method.

FIG. 9A shows another configuration example of a first illumination unitand an intensity-distribution changing unit.

FIG. 9B shows another configuration example of the first illuminationunit and the intensity-distribution changing unit.

FIG. 9C shows another configuration example of the first illuminationunit and the intensity-distribution changing unit.

FIG. 10 is a diagram showing the relationships between the shapes of thewavelength spectra of the first and second illumination light; and thecontrasts of the surface-layer component image and the deep-layercomponent image.

FIG. 11 shows another configuration example of the first illuminationunit and the second illumination unit.

FIG. 12 is a shows the configuration of a part of a modification of anendoscope system having a polarizer.

FIG. 13 is a diagram showing the relationship between: the distance Dbetween the first and second exit faces; and the distance L from thefirst and second exit faces to biological tissue.

FIG. 14 is a diagram showing the relationships between D/L and noise inthe surface-layer image and the deep-layer image and shows examples ofthe surface-layer image and the deep-layer image with different D/Ls.

FIG. 15 is a deep-layer image with D/L=0.113.

FIG. 16 is a gradation value profile taken along line I-I in FIG. 15.

FIG. 17 is a graph showing the relationship between D/L and the numberof pixels with a gradation value of less than or equal to 70.

DESCRIPTION OF EMBODIMENTS

An endoscope system 1 according to an embodiment of the presentinvention will be described below with reference to the drawings.

As shown in FIG. 1, the endoscope system 1 according to this embodimentincludes an endoscope 2 for observing the inside of the body, and a bodypart 3 connected to the base end of the endoscope 2.

The endoscope system 1 also includes a first illumination unit 41 and asecond illumination unit 42 that emit illumination light L1 and L2 fromthe distal end of the endoscope 2 toward biological tissue (subject) Ainside the body, an intensity-distribution changing unit 5 that changesthe intensity distribution of the first illumination light L1 with time,an imaging unit 6 that images first and second illumination images ofthe biological tissue A illuminated with the illumination light L1 andL2, and an image processing unit 7 that processes the first and secondillumination images imaged by the imaging unit 6 to generate twoseparated images having information at different depths in thebiological tissue A.

The first illumination unit 41 has a first exit face 41 a provided atthe distal end face of the endoscope 2 and emits, from the first exitface 41 a to the biological tissue A, white first illumination light L1having a spatially non-uniform intensity distribution in a beamcross-section perpendicular to the optical axis. Typically, the firstillumination light L1 has such an intensity gradient that the brightnessgradually decreases from the center of the beam toward the periphery.Besides this overall intensity gradient at the beam cross-section, thefirst illumination light L1 has, at the beam cross-section, a structuredlight/dark pattern, in which high-intensity light portions and darkportions, which have lower intensity than the light portions or have nointensity, are alternately repeated.

This first illumination unit 41 includes a light source 41 b provided inthe body part 3, a mask 41 c, a light-collecting lens 41 d, and,provided in the endoscope 2, an image guide fiber 41 e and a projectionlens 41 f.

The light source 41 b is a semiconductor light source, using, forexample, an LED or an LD. Alternatively, the light source 41 b may be anexit end of an optical fiber connected to a light source device (notshown) outside the body part 3.

The mask 41 c is a liquid-crystal element whose light transmittance atrespective positions in an incident area, on which white light isincident, can be electrically controlled, and a projection patternincluding light-transmission areas, which allow the white light to passtherethrough, and light-blocking areas, which block the white light, andcorresponding to the light/dark pattern is formed thereon. The whitelight output from the light source 41 b is provided with a light/darkpattern as it passes through the mask 41 c and becomes the firstillumination light L1. The thus-generated first illumination light L1 isfocused at the entrance end of the image guide fiber 41 e by thelight-collecting lens 41 d because the size of the starting point at thesubject-side distal end portion of the endoscope 2 needs to be reduced.The first illumination light L1 is then guided to the projection lens 41f provided at the distal end of the endoscope 2 through the image guidefiber 41 e while preserving the light/dark pattern and is emitted as adivergent beam from the first exit face 41 a, which is the distal endface of the projection lens 41 f, by the projection lens 41 f.

The second illumination light L2 is wideband white light having aspectrum covering substantially the entire visible band. The secondillumination unit 42 has a second exit face 42 a provided at the distalend face of the endoscope 2 and emits, from the second exit face 42 a tothe biological tissue A, white second illumination light L2 having aspatially substantially uniform intensity distribution in a beamcross-section perpendicular to the optical axis. The second exit face 42a is disposed beside the first exit face 41 a. This second illuminationunit 42 includes a light source 42 b provided in the body part 3, and abundle fiber 42 c and a projection lens 42 d provided in the endoscope2.

The light source 42 b is a semiconductor light source using, forexample, an LED or an LD or a lamp light source, such as a xenon lamp.The white light may be generated by mixing red, green, and blue lightoutput from a plurality of light sources 42 b. The white light outputfrom the light source 42 b is guided to the projection lens 42 d,provided at the distal end of the endoscope 2, through the bundle fiber42 c and is emitted as a divergent beam from the second exit face 42 a,which is the distal end face of the projection lens 42 d, by theprojection lens 42 d.

The first illumination unit 41 and the second illumination unit 42 arecontrolled by a control unit (not shown) provided in the body part 3 soas to alternately emit the first illumination light L1 and the secondillumination light L2 toward the biological tissue A.

The intensity-distribution changing unit 5 is a control device forcontrolling the light transmittance at the respective positions in theincident area of the mask 41 c and changes, with time, the intensitydistribution of the first illumination light L1 such that the lightportions and the dark portions are switched at the beam cross-section.This allows the light portions and the dark portions to be alternatelyprojected, in order, at the respective positions in the irradiation areaof the first illumination light L1 on the surface B of the biologicaltissue A.

FIGS. 2A to 2F each show an example light/dark pattern of the intensitydistribution of the first illumination light L1 and the temporal changethereof. In FIGS. 2A to 2F, the white areas show the light portions, andthe black areas show the dark portions.

The light/dark pattern in FIG. 2A is a checkered pattern in which squarelight portions and dark portions are alternately repeated in twodirections perpendicular to each other.

The light/dark patterns in FIGS. 2B and 2C are stripe patterns in whichlinear band-like light portions and dark portions are alternatelyrepeated only in the width direction, which is perpendicular to thelongitudinal direction of the light portions and the dark portions. Inthe stripe patterns, the spatial period of the light portions and thedark portions may be either regular, as shown in FIG. 2B, or irregular,as shown in FIG. 2C.

The light/dark pattern in FIG. 2D is a stripe pattern in which wave-likeband-like light portions and dark portions are alternately repeated onlyin the width direction, which is perpendicular to the longitudinaldirection of the light portions and the dark portions.

The light/dark pattern in FIG. 2E is a dot pattern in which the lightportions or the dark portions are circles, and the other is thebackground.

The light/dark pattern in FIG. 2F is a concentric circle pattern inwhich circular band-like light portions and dark portions arealternately repeated in the radial direction.

FIGS. 3A to 3F show example intensity profiles showing spatial changesin the intensity I between the light portions and the dark portions inthe light/dark patterns in FIGS. 2A to 2F. The horizontal axis shows theposition X. The intensity profile may have a rectangular-wave shape, asshown in FIG. 3A, a sine-wave shape, as shown in FIG. 3B, a shapebetween a rectangular wave and a sine wave, as shown in FIGS. 3C and 3D,or an asymmetric wave shape, as shown in FIG. 3E. As shown in FIG. 3E,the intensity profile may be highest at the center of the firstillumination light L1 and may generally decrease from the center towardthe periphery. In each of FIGS. 3A to 3E, the period of the lightportions and the dark portions may be the distance between a lightportion and an adjoining light portion.

The imaging unit 6 includes an imaging lens 6 a provided at the distalend of the endoscope 2 to collect light produced by the biologicaltissue A, and an imaging element 6 b for imaging an image of thebiological tissue A formed by the imaging lens 6 a. The imaging unit 6performs imaging while the first illumination light L1 is radiated ontothe biological tissue A to image a first illumination image and performsimaging while the second illumination light L2 is radiated onto thebiological tissue A to image a second illumination image. Therefore, theoperations of the illumination units 41 and 42 and the imaging element 6b are controlled by the control unit such that the timing for emittingthe illumination light L1 and L2 from the illumination units 41 and 42and the timing for imaging images with the imaging element 6 b aresynchronized. The first illumination image and the second illuminationimage imaged by the imaging element 6 b are transmitted from the imagingelement 6 b to the image processing unit 7.

Herein, the intensity distribution of the first illumination light L1radiated onto the biological tissue A is changed with time by theintensity-distribution changing unit 5, as shown in FIGS. 2A to 2F. Byperforming imaging operations at two times at which the light portionsand the dark portions of the first illumination light L1 radiated ontothe biological tissue A are reversed, the imaging element 6 b images twofirst illumination images in which light-portion projected areas anddark-portion projected areas are reversed so that the light-portionprojected areas and the dark-portion projected areas compensate for eachother, as shown in FIG. 4. In the first illumination images in FIG. 4,the white areas represent the light-portion projected areas, and theblack areas represent the dark-portion projected areas. Accordingly, theoperations of the intensity-distribution changing unit 5 and the imagingelement 6 b are controlled by the control unit such that the timing forchanging the intensity distribution with the intensity-distributionchanging unit 5 and the timing for imaging images with the imagingelement 6 b are synchronized.

The image processing unit 7 includes, as functions, a separationprocessing unit 71 that separates a surface-layer component image (imageinformation) and a deep-layer component image (image information) fromthe two first illumination images, and a separated-image generating unit72 that processes the second illumination image using the surface-layercomponent image and the deep-layer component image to generate asurface-layer image (separated image) and a deep-layer image (separatedimage).

FIG. 4 shows image processing performed by the separation processingunit 71. For the pixel located at each position in the two firstillumination images, an intensity value Imax corresponding to when alight portion is projected and an intensity value Imin corresponding towhen a dark portion is projected are imaged. As shown in FIG. 4, theseparation processing unit 71 generates a deep-layer component imagecontaining a large amount of information about a deep layer D of thebiological tissue A from the intensity values Imin in the two firstillumination images and generates a surface-layer component imagecontaining a large amount of information about a surface B and a surfacelayer C of the biological tissue A from the intensity values Imin andthe intensity values Imax in the two first illumination images.

The biological tissue A is a scatterer and includes, as shown in FIG. 5,structures α, such as capillaries, in the surface layer C extending fromthe surface B to a depth of several tens of μm and structures β, such aslarge blood vessels, in the deep layer D located at a deeper part thanthe surface layer C. When the first illumination light L1 having alight/dark pattern is radiated on the biological tissue A, thebiological tissue A generates specular reflection (specular) light Lr,surface scattered light Ls, and internal scattered light Ld. In FIG. 5,the illustration of the second illumination unit 42 is omitted.

The specular light Lr is reflected light of the first illumination lightL1 specularly reflected at the surface B of the biological tissue A andis generated at the light-portion projected areas.

The surface scattered light Ls is scattered light of the firstillumination light L1 that has entered the biological tissue A from thelight-portion projected areas, has passed through the surface layer Cwhile being repeatedly scattered, and has been emitted from the surfaceB. Most of the surface scattered light Ls is emitted from thelight-portion projected areas.

The internal scattered light Ld is scattered light of the firstillumination light L1 that has entered the biological tissue A from thelight-portion projected areas, has passed through the deep layer D whilebeing repeatedly scattered, and has been emitted from the surface B. Aportion of the internal scattered light Ld is emitted from thelight-portion projected areas, and another portion is emitted from thedark-portion projected areas after propagating to the dark-portionprojected areas.

As described, the intensity values Imin at the dark-portion projectedareas in the two first illumination images are mainly based on theinternal scattered light Ld and mainly contain information about thedeep layer D. Meanwhile, the intensity values Imax at the light-portionprojected areas in the two first illumination images are based on thespecular light Lr, the surface scattered light Ls, and the internalscattered light Ld and contain information about the surface B, thesurface layer C, and the deep layer D.

FIG. 6 shows a detailed method for generating a surface-layer componentimage and a deep-layer component image by the separation processing unit71. As shown in FIG. 6, the two first illumination images havebrightness distributions in which the intensity value is high at pixelscorresponding to the light-portion projected areas, and the intensityvalue is low at pixels corresponding to the dark-portion projectedareas. To simplify the explanation, FIG. 6 shows intensity profiles inthe cases where the first illumination light L1 has a light/dark patternin which, as in the light/dark pattern in FIG. 2A or 2B, the lightportions and the dark portions are repeated at regular periods, and theboundaries between the pixels in the image and the boundaries betweenthe light portions and the dark portions in the light/dark patterncoincide (that is, one light portion or dark portion corresponds to onepixel).

As described above, for each pixel, two intensity values, Imax and Imin,can be obtained from the two first illumination images. For each pixel,the separation processing unit 71 defines the higher intensity value asthe intensity value Imax and the lower intensity value as the intensityvalue Imin. Next, the separation processing unit 71 calculates anintensity value Is of each pixel of the surface-layer component imageand an intensity value Id of the pixel of the deep-layer component imagefrom the expression below to generate a surface-layer component imagehaving the intensity value Is and a deep-layer component image havingthe intensity value Id.Is=Imax−IminId=Imin×2

As a result, a deep-layer component image having the intensity valueImin, which mainly contains information about the deep layer D, isgenerated. By subtracting the intensity value Imin from the intensityvalue Imax, the information about the deep layer D is removed, and asurface-layer component image having the intensity value Is, whichmainly contains information about the surface B and the surface layer C,is generated.

As shown in FIG. 7, the separated-image generating unit 72 generates asurface-layer image on the basis of Expression (a) below and generates adeep-layer image on the basis of Expression (b) below.Surface-layer image=second illumination image×surface-layer componentimage/(surface-layer component image+deep-layer component image)  (a)Deep-layer image=second illumination image×deep-layer componentimage/(surface-layer component image+deep-layer component image)  (b)

Specifically, the separated-image generating unit 72 generates asurface-layer image by calculating the proportion of the surface-layercomponent image in the sum of the surface-layer component image and thedeep-layer component image and multiplying the calculated proportion bythe second illumination image. The separated-image generating unit 72generates a deep-layer image by calculating the proportion of thedeep-layer component image in the sum of the surface-layer componentimage and the deep-layer component image and multiplying the calculatedproportion by the second illumination image.

The surface-layer image and the deep-layer image generated by theseparated-image generating unit 72 are output from the body part 3 to adisplay device (not shown) connected to the body part 3 and aredisplayed on the display device.

This image processing unit 7 is realized as, for example, an imageprocessing program executed by a computer. Specifically, the body part 3accommodates a central processing unit (CPU), a main memory, such as aRAM, and an auxiliary storage, such as a hard-disk drive. An imageprocessing program for causing the CPU to execute the above-describedprocessing by the image processing unit 7 is stored in the auxiliarystorage. As a result of the image processing program being loaded fromthe auxiliary storage into the main memory, and the CPU executing theprocessing in accordance with the image processing program, theabove-described function of the image processing unit 7 is realized.

When the second illumination light L2, which is ordinary white lighthaving a spatially substantially uniform intensity distribution, isradiated onto the biological tissue A, the specular light Lr, thesurface scattered light Ls, and the internal scattered light Ld enterthe imaging unit 6 in a superimposed state. Hence, the secondillumination image, which is obtained by imaging an image of thebiological tissue A illuminated with the second illumination light L2,shows both the structures α, such as capillaries, in the surface layer Cextending from the surface B to a depth of several tens of μm and thestructures β, such as large blood vessels, in the deep layer D.

In contrast, when the first illumination light L1 having a light/darkpattern is radiated onto the biological tissue A, the internal scatteredlight Ld containing a large amount of information about the deep layer Dis spatially separated from the specular light Lr and the surfacescattered light Ls containing information about the surface B and thesurface layer C, and a first illumination image, in which the area wherethe information about the deep layer D is dominant is spatiallyseparated from the area containing a large amount of information aboutthe surface B and the surface layer C, is obtained. From this firstillumination image, a surface-layer component image, which mainlycontains information about the surface B and the surface layer C and inwhich images of the structures α are emphasized, and a deep-layercomponent image, which mainly contains information about the deep layerD and in which images of the structures β are emphasized, can beseparated.

Although it may be difficult to ensure a sufficient level of structuredfirst illumination light L1 due to the design limitation or the like ofthe first illumination unit 41, it is easy to ensure a sufficient levelof second illumination light L2, which is ordinary white light, andthus, it is possible to image a bright second illumination image.According to this embodiment, by correcting this bright secondillumination image with the surface-layer component image and thedeep-layer component image to generate the surface-layer image and thedeep-layer image, a bright surface-layer image and a deep-layer imagecan be generated, which is advantageous.

The amount of information about the surface layer C in the surface-layerimage and the amount of information about the deep layer D in thedeep-layer image depend on the width Wd (see FIG. 5) of the darkportions on the surface B of the biological tissue A. More specifically,the larger the width Wd of the dark portions is, the larger the amountof information about the surface layer C that can be imaged as thesurface-layer image is, because the depth of the surface layer C isgreater than that when the width Wd of the dark portions is small,whereas the larger the width Wd of the dark portions is, the less theamount of information about the deep layer D is, because the depth ofthe deep layer D is constant regardless of the width Wd of the darkportions. To ensure good balance between the amount of information aboutthe surface layer C in the surface-layer image and the amount ofinformation about the deep layer D in the deep-layer image, it isdesirable that the width Wd of the dark portions on the surface B of thebiological tissue A be from 0.005 mm to 25 mm.

When the width Wd of the dark portions is less than 0.005 mm, theproportion of the internal scattered light Ld that spreads from thelight-portion projected areas into the dark-portion projected areasincreases. As a result, the difference between the intensity value Imaxand the intensity value Imin decreases, potentially leading to a lack ofinformation about the surface layer C contained in the surface-layercomponent image and the surface-layer image. On the other hand, when thewidth Wd of the dark portions is greater than 25 mm, the internalscattered light Ld cannot reach the central portions of the dark-portionprojected areas. As a result, the intensity value Imin approaches zero,potentially leading to a lack of information about the deep layer Dcontained in the deep-layer component image and the deep-layer image.

In this embodiment, in generating the surface-layer image, theseparated-image generating unit 72 may multiply the surface-layercomponent image by a coefficient P, as shown in Expression (a′) below.In generating the deep-layer image, the separated-image generating unit72 may multiply the deep-layer component image by a coefficient Q, asshown in Expression (b′) below.Surface-layer image=second illumination image×P×surface-layer componentimage/(surface-layer component image+deep-layer component image)  (a′)Deep-layer image=second illumination image×Q×deep-layer componentimage/(surface-layer component image+deep-layer component image)  (b′)

This makes it possible to generate a surface-layer image in whichinformation about the surface layer is further emphasized in accordancewith the coefficient P and to generate a deep-layer image in whichinformation about the deep layer is further emphasized in accordancewith the coefficient Q.

The separated-image generating unit 72 may also combine thesurface-layer image and the deep-layer image to generate a combinedimage. In this case, by setting one of the coefficients P and Q to alarge value, it is possible to generate a combined image in which one ofthe information about the surface layer C and the information about thedeep layer D is emphasized, while preserving both sets of information.More specifically, by increasing the coefficient P, it is possible toobtain a combined image in which the information about the surface layerC is emphasized, and by increasing the coefficient Q, it is possible toobtain a combined image in which the information about the deep layer Dis emphasized. Similarly, by setting one of the coefficients P and Q toa small value, it is possible to generate a combined image in which oneof the information about the surface layer C and the information aboutthe deep layer D is deemphasized while preserving both sets ofinformation.

For example, the coefficients P and Q are set by a user through inputmeans (not shown) connected to the body part 3.

The coefficients P and Q may be set for each pixel. The intensity valueIij of each pixel ij in the combined image can be calculated from theexpression below. Herein, ij (i=1, 2, . . . , n, j=1, 2, . . . , m) arethe position coordinates of a pixel in an image of n pixels×m pixels. Inthe expression below, Pij is the combining ratio of the pixels ij in thesurface-layer image, and Qij is the combining ratio of the pixels ij inthe deep-layer image.Iij=Pij*Isij/(Isij+Idij)+Qij*Idij/(Isij+Idij)

For example, the system may be configured such that a user can set thecombining ratios Pij and Qij while observing the surface-layer image andthe deep-layer image displayed on the display device.

The coefficients P and Q may be set for each wavelength. The intensityvalue Ik of a wavelength λk (k=1, 2, . . . , 1) of a combined image canbe calculated from the expression below. Isk is the intensity value ofthe wavelength λk of the surface-layer image, Idk is the intensity valueof the wavelength λk of the deep-layer image, Pk is the combining ratioof the wavelength λk of the surface-layer image, and Qk is the combiningratio of the wavelength λk of the deep-layer image.Ik=Pk*Isk/(Isk+Idk)+Qk*Idk/(Isk+Idk)

For example, the system may be configured such that a user can set thecombining ratios Pk and Qk while observing the surface-layer image andthe deep-layer image displayed on the display device.

In this embodiment, although the intensity-distribution changing unit 5may alternately change, in a discontinuous manner, the intensitydistribution of the first illumination light L1 between two light/darkpatterns in which the light portions and the dark portions are reversed,as shown in FIGS. 2A to 2F, instead, the intensity-distribution changingunit 5 may change the intensity distribution of the first illuminationlight L1 between the two light/dark patterns in a continuous manner.

When the light/dark pattern is change in a continuous manner like this,the imaging unit 6 may perform imaging at three or more different timesat which the positions of the light portions and the dark portions aredifferent from each to image three or more first illumination images inwhich the positions of the light-portion projected areas and thedark-portion projected areas are different from each other. Theseparation processing unit 71 may generate the surface-layer componentimage and the deep-layer component image from the three or more firstillumination images. In this case, because three or more intensityvalues are obtained for the pixel at each position, the maximumintensity value may be calculated as Imax, and the minimum intensityvalue may be calculated as Imin.

In this embodiment, although the intensity values in the two firstillumination images are used as the intensity values Imax and Imin, whenthe light/dark pattern is a linear stripe pattern in which the intensitychanges in the form of a sine wave, as shown in FIGS. 2B and 3B, theintensity values Imax and Imin of each pixel may be calculated by usinga phase shift method. By using the phase shift method, the maximumintensity value Imax and the minimum intensity value Imin of each pixelcan be calculated from three first illumination images having differentlight/dark pattern phases Φ, as shown in FIG. 8. Accordingly, it ispossible to generate a surface-layer image and a deep-layer image havingthe same resolution as the second illumination image by using a smallnumber of first illumination images.

In this embodiment, although the first illumination light L1 having alight/dark pattern structured by the liquid-crystal element provided inthe body part 3 is generated, the configuration of the firstillumination unit 41 is not limited thereto, and the first illuminationlight L1 may be generated by another method.

FIGS. 9A to 9C show modifications of the configuration of the firstillumination unit 41 and the intensity-distribution changing unit 5.

The first illumination unit 41 in FIG. 9A forms a light/dark pattern onthe surface B of the biological tissue A as in a shadowgraph andincludes a light source 41 b and a mask 41 g provided at the distal endportion of the endoscope 2.

The mask 41 g is, for example, a light-shielding substrate provided withopenings, serving as light-transmission areas, or a transparentsubstrate provided with a light-shielding film, serving aslight-blocking areas. When the white light output from the light source41 b passes through the mask 41 g, the first illumination light L1having a light/dark pattern is generated, and the projection pattern ofthe mask 41 g is projected on the biological tissue A. A lens 41 h thatchanges the divergence angle of the white light such that theillumination light L1 radiated on the biological tissue A has a desireddivergence angle may be provided between the light source 41 b and themask 41 g.

By making the intensity-distribution changing unit 5 serve as anactuator for moving at least one of the light source 41 b and the mask41 g to relatively move the light source 41 b and the mask 41 g in adirection intersecting the optical axis of the white light, theintensity distribution can be changed with time.

The intensity-distribution changing unit 5 may alternatively be made toserve as a control device for controlling turning on and off of aplurality of light sources 41 b so as to turn on some of the lightsources 41 b, instead of moving a single light source 41 b.Specifically, by arraying the plurality of light sources 41 b in adirection substantially parallel to the mask 41 g and making theintensity-distribution changing unit 5 switch the light sources 41 b tobe turned on, it is possible to change the intensity distribution withtime.

The first illumination unit 41 in FIG. 9B uses an interference fringe oflight as the light/dark pattern and includes a laser light source 41 iand an optical path 41 j that splits the light output from the laserlight source 41 i into two and emits two rays of light. The optical path41 j is formed of, for example, an optical fiber. When the two rays oflight emitted from the optical path 41 j interfere with each other,interference fringes having a sine-wave-shaped intensity profile,serving as a light/dark pattern, are formed. The intensity-distributionchanging unit 5, which is provided in one of the optical paths of thetwo rays of light split, is an optical device that changes the opticalpath length. The intensity-distribution changing unit 5 shifts theposition of the interference fringes in a direction perpendicular to theoptical axis of the illumination light by changing the length of one ofthe optical paths of the two rays of light.

The first illumination unit 41 in FIG. 9C includes a light source array41 k and a light guide member 411 that guides the light while preservingthe angle of incidence of the light with respect to the optical axisthereof. The light source array 41 k has a plurality of light sources 41b arranged such that the angles of incidence of light with respect tothe entrance end of the light guide member 411 are different from eachother. Although the plurality of light sources 41 b are arranged in aline in FIG. 9C, the plurality of light sources 41 b may be arrangedtwo-dimensionally. An example light guide member 411 is a rod lens or amulti-mode fiber.

The rays of white light emitted from the light sources 41 b areconverted into parallel beams by the lens 41 m and enter the entranceend of the light guide member 411. The beams that have entered the lightguide member 411 are guided through the light guide member 411 whilepreserving their angles and are emitted from the exit end of the lightguide member 411 toward the biological tissue A at the same angles asthe angles at which the beams entered the entrance end. Because thebeams diffuse in the circumferential direction while being repeatedlyreflected in the light guide member 411, the beams emitted from thelight guide member 411 form a circular shape. Accordingly, bysimultaneously turning on the plurality of light sources 41 b, firstillumination light L1 having a concentric circle pattern, as shown inFIG. 2F, is generated.

The intensity-distribution changing unit 5 is a control device forcontrolling turning on and off of the light sources 41 b. Theintensity-distribution changing unit 5 changes the intensitydistribution by controlling turning on and off of the respective lightsources 41 b to switch the light sources 41 b to be turned on.

Instead of switching the light sources 41 b to be turned on, theintensity-distribution changing unit 5 may be made to serve as anactuator for moving the light sources 41 b in a direction intersectingthe optical axis.

In this embodiment, it is desirable that the first illumination unit 41emit divergent first illumination light L1 toward the biological tissueA such that the light/dark pattern projected on the surface B of thebiological tissue A is magnified in proportion to the imaging distancebetween the biological tissue A and the imaging unit 6.

The boundary between the depth of the information contained in thesurface-layer component image and the depth of the information containedin the deep-layer component image depends on the period of the lightportions and the dark portions. The larger the period of the lightportions and the dark portions is, the deeper the position of theboundary is, and thus, the larger the amount of information contained inthe surface-layer component image is. Accordingly, by changing theimaging distance to magnify or reduce the light/dark pattern on thesurface B of the biological tissue A, the surface-layer component imageand the deep-layer component image containing the information atdifferent depths can be imaged.

Although the period of the light portions and the dark portions on thesurface B of the biological tissue A may be changed by changing theimaging distance to magnify or reduce the overall light/dark pattern,the spatial period of the light portions and the dark portions in thelight/dark pattern of the first illumination light L1 may be changed.

For example, the period of the light portions and the dark portions maybe changed by electrically controlling the liquid-crystal element 41 cprovided in the first illumination unit 41.

Three or more separated images may be generated by using two or morefirst illumination images imaged by radiating the first illuminationlight L1 in which the spatial period of the light portions and the darkportions, that is, the width of the dark portions, varies. Specifically,the separation processing unit 71 may separate three or more componentimages containing information at different depths from two or more firstillumination images, and the separated-image generating unit 72 maygenerate three or more separated images containing information atdifferent depths by using the three or more component images.

When the light/dark pattern is formed by means of projection, as shownin FIG. 9A, the period of the light portions and the dark portions maybe changed by relatively moving the light sources 41 b and the mask 41 gin the optical axis direction of the white light to change the distancebetween the light sources 41 b and the mask 41 g.

Alternatively, a zoom lens including a plurality of lenses, at least oneof which is movable in the optical axis direction, may be provided onthe optical path of the first illumination light L1.

Although the first illumination unit 41 emits the white firstillumination light L1 in this embodiment, the first illumination lightL1 is not limited to the white light and may be light having otherwavelength characteristics. Examples of the first illumination light L1include infrared light, monochromatic light, such as red, green, or bluelight, and light having a single wavelength. Alternatively, the firstillumination light L1 may be composed of a plurality of light havingdifferent wavelengths and may be, for example, white light formed bymixing three light, namely, red, green and blue light.

The shape of the wavelength spectrum of the first illumination light L1may be different from the shape of the wavelength spectrum of the secondillumination light L2.

In general, light having a shorter wavelength is more strongly scatteredby a scatterer. Accordingly, short wavelength light is less likely toreach the deep layer D of the biological tissue A than long wavelengthlight, and the information contained in the internal scattered light Ldof the short wavelength light is information at a position shallowerthan the internal scattered light Ld of the long wavelength light.

FIG. 10 schematically shows the relationships between the shapes of thewavelength spectra of the illumination light L1 and L2 and the contrastsof the surface-layer component image and the deep-layer componentimages.

As shown in the top row in FIG. 10, when the shape of the wavelengthspectrum of the first illumination light L1 is the same as the shape ofthe wavelength spectrum of the second illumination light L2, thecontrasts of the surface-layer component image and the deep-layercomponent image are substantially equal to each other. Hence, by usingthe surface-layer component image and the deep-layer component image inthis state, a natural surface-layer image and deep-layer image can begenerated.

On the other hand, as shown in the middle row in FIG. 10, by using thefirst illumination light L1 having an intensity distribution shiftedtoward the short wavelength side compared with the second illuminationlight L2, it is possible to generate a surface-layer image in which thecontrast of the surface-layer component image is increased to furtheremphasize the information about the surface layer. Furthermore, as shownin the bottom row in FIG. 10, by using the first illumination light L1having an intensity distribution shifted toward the long wavelength sidecompared with the second illumination light L2, it is possible togenerate a deep-layer image in which the contrast of the deep-layercomponent image is increased to further emphasize the information aboutthe deep layer.

Although the information about the surface layer in the surface-layerimage and the information about the deep layer in the deep-layer imagecan also be emphasized by increasing the coefficients P and Q asdescribed above, by controlling the wavelength of the first illuminationlight L1, it is possible to generate a surface-layer image and adeep-layer image that does not evoke a feeling of strangeness, unlikethe electrical emphasis as described above.

When light, such as infrared light, having a different wavelength bandfrom the wavelength band of the second illumination light L2 is used asthe first illumination light L1, the first illumination unit 41 and thesecond illumination unit 42 may simultaneously radiate the firstillumination light L1 and the second illumination light L2 onto thebiological tissue A, and the imaging unit 6 may image images of thebiological tissue A irradiated with both the first illumination light L1and the second illumination light L2 to simultaneously image the firstillumination image and the second illumination image. The imaging unit 6is configured to separate the light produced by the biological tissue Aby being irradiated with the first illumination light L1 and the lightproduced by the biological tissue A by being irradiated with the secondillumination light L2 in accordance with the wavelength and toseparately image images thereof.

By imaging the first illumination image and the second illuminationimage in a single imaging operation like this, it is possible toincrease the frame rate of the surface-layer image and the deep-layerimage.

In this embodiment, although the first illumination unit 41 and thesecond illumination unit 42 have the light source 41 b and the lightsource 42 b, respectively, instead, as shown in FIG. 11, the firstillumination unit 41 and the second illumination unit 42 may have asingle common light source 4 a. The white light output from the lightsource 4 a is divided into two by a half mirror HM and is distributedbetween the first illumination unit 41 and the second illumination unit42.

By making the first illumination unit 41 and the second illuminationunit 42 use a common light source as in this configuration, firstillumination light L1 and second illumination light L2 having the samewavelength spectrum can be generated. By reducing the number of thelight sources 4 a, the cost and size of the device can be reduced.

In this embodiment, although the information about the biological tissueA is separated into two, namely, the information about the surface B andthe surface layer C and the information about the deep layer D, it ispossible to further separate the information about the surface B and theinformation about the surface layer C by using polarization, as shown inFIG. 12. In FIG. 12, the illustration of the second illumination unit 42is omitted.

The endoscope 2 includes, at the distal end thereof, a polarizer 9 thatcontrols the polarizing state of the first illumination light L1 emittedfrom the first illumination unit 41, and a polarizer 10 that selects thepolarizing state of the light produced by the biological tissue A andentering the imaging unit 6. By aligning the polarizing direction of thepolarizer 10 with the polarizing direction of the polarizer 9, a firstillumination image containing the surface scattered light Ls and thespecular light Lr can be imaged, and, by arranging the polarizingdirection of the polarizer 10 perpendicular to the polarizing directionof the polarizer 9, a first illumination image not containing thespecular light Lr, but containing the surface scattered light Ls can beimaged.

In this embodiment, it is desirable that Expression (1) below besatisfied. As shown in FIG. 13, in Expression (1), D is the distance(center-to-center distance) between the first exit face 41 a and thesecond exit face 42 a, and L is the distance from the first exit face 41a and the second exit face 42 a (distal end face of the endoscope 2) tothe biological tissue A. The distance L is set to a value within anappropriate range according to the focal distance of the endoscope 2.D/L<0.068  (1)

Due to the difference in position between the first exit face 41 a andthe second exit face 42 a, the position of the specular light in thefirst illumination image and the position of the specular light in thesecond illumination image differ. When the first and second illuminationimages in which the positions of the specular light are different areused to generate a surface-layer image and a deep-layer image, white(i.e., high-gradation-value) spot-like noise occurs in the surface-layerimage, and black (i.e., low-gradation-value) spot-like noise occurs inthe deep-layer image. As shown in FIG. 14, the noise is more noticeablewhen the distance D between the exit faces 41 a and 42 a is larger orwhen the distance L from the exit faces 41 a and 42 a to the biologicaltissue A is smaller. FIG. 14 shows example surface-layer images anddeep-layer images when D/L=0, 0.023, 0.045, 0.068, and 0.113.

FIG. 15 shows a deep-layer image when D/L=0.113, and FIG. 16 is agradation value profile taken along line I-I in FIG. 15. As shown inFIG. 16, the gradation values of the black spots, which are noise, areless than or equal to 70.

FIG. 17 is a graph showing the relationship between the D/L value(horizontal axis) and the number of pixels having a gradation value ofless than or equal to 70 in the deep-layer image (vertical axis). Thegraph shows that the number of pixels having a gradation value of lessthan or equal to 70, which represent black spots, tends to be small inthe area satisfying D/L<0.068. This is because, when D/L<0.068 issatisfied, the position of the specular light in the first illuminationimage and the position of the specular light in the second illuminationimage substantially coincide. Accordingly, the black-spot noise in thedeep-layer image can be prevented by satisfying Expression (1). For thesame reason, the white-spot noise in the surface-layer image can beprevented by satisfying Expression (1).

As a result, the following aspect is read from the above describedembodiment of the present invention.

An aspect of the present invention is an endoscope system including: afirst illumination unit that emits, from a first exit face to a subject,first illumination light for imaging two sets of image information aboutthe subject at different depths; a second illumination unit that emits,from a second exit face disposed at a different position from the firstexit face to the subject, second illumination light having a wide bandcovering a visible band; an imaging unit that images a firstillumination image of the subject illuminated with the firstillumination light, and a second illumination image of the subjectilluminated with the second illumination light; a separation processingunit that separates the two sets of image information from the firstillumination image; and a separated-image generating unit that processesthe second illumination image using the two sets of image information togenerate two separated images each containing a large amount ofinformation about the subject at the different depths.

According to this aspect, the second illumination image is imaged as aresult of the imaging unit imaging an image of the subject illuminatedwith the second illumination light emitted from the second exit face.Meanwhile, the first illumination image is imaged as a result of theimaging unit imaging an image of the subject illuminated with the firstillumination light emitted from the first exit face, and the separationprocessing unit separates two sets of image information at differentdepths contained in the first illumination image. By processing thesecond illumination image using the two sets of image information, it ispossible to generate two separated images containing information aboutthe subject at different depths.

In this case, because it is possible to brightly illuminate the subjectwith the second illumination unit, which is provided separately from thefirst illumination unit for imaging image information at differentdepths, it is possible to image a bright second illumination image.Based on this bright second illumination image, a bright separated imagecan be obtained.

In the above-described aspect, the first illumination light may have aspatially non-uniform intensity distribution including light portionsand dark portions in a beam cross-section perpendicular to the opticalaxis.

When illumination light is radiated onto a subject that is a scatterer,specular reflection (specular) light specularly reflected at the surfaceof the subject, surface scattered light scattered in a surface layerinside the subject and emitted from the surface of the subject, andinternal scattered light scattered in a deep layer inside the subjectand emitted from the surface of the subject are produced. By radiatingthe first illumination light having a spatially non-uniform intensitydistribution onto the subject, the internal scattered light is spatiallyseparated from the specular light and the surface scattered light.Specifically, the specular light, the surface scattered light, and theinternal scattered light are produced in the light portions, whereas theinternal scattered light that spreads from the light portions to thedark portions is dominantly produced in the dark portions. Accordingly,it is possible to separate the image information at the deep layer fromthe areas corresponding to the dark portions in the first illuminationimage and to separate the image information at the surface and thesurface layer from the areas corresponding to the light portions in thefirst illumination image.

In the above-described aspect, the light portions and the dark portionsincluded in the first illumination light may be band-shaped, and thelight portions and the dark portions may be alternately repeated in awidth direction, forming a stripe shape.

This makes it possible to effectively separate the internal scatteredlight with a simple light/dark pattern. Furthermore, to switch thepositions of the light portions and the dark portions of the stripeintensity distribution, it is only necessary to move the light portionsand dark portions of the intensity distribution only in the widthdirection of the stripe. Hence, it is possible to easily change theintensity distribution of the illumination light with time.

In the above-described aspect, the light portions and the dark portionsincluded in the first illumination light may have a substantiallysine-wave-shaped intensity profile in the width direction.

By radiating such first illumination light having an intensity spatiallychanging in a sine-wave shape, it is possible to calculate, by using aphase shift method, the intensity value for a separated image of thesurface layer when irradiated with the highest-intensity light and theintensity value for a separated image of the deep layer when irradiatedwith no light. Hence, it is possible to generate high-resolutiongood-quality separated images even from a small number of firstillumination images.

In the above-described aspect, the shape of the wavelength spectrum ofthe first illumination light may be that of a single wavelength.

In the above-described aspect, the wavelength spectrum of the firstillumination light and the wavelength spectrum of the secondillumination light may have different shapes.

This makes it possible to image a first illumination image containing alarger amount of information at a specific depth in accordance with theshape of the wavelength spectrum of the first illumination light andthus to generate a separated image in which information at the specificdepth is further emphasized.

In the above-described aspect, the first illumination light and thesecond illumination light may have different wavelength bands.

This makes it possible to image a first illumination image containing alarger amount of information at a specific depth corresponding to thewavelength band of the first illumination light and thus to generate aseparated image in which information at the specific depth is furtheremphasized.

In the above-described aspect, the wavelength band of the firstillumination light may be an infrared band.

In the above-described aspect, the first illumination unit and thesecond illumination unit may simultaneously emit the first illuminationlight and the second illumination light.

This makes it possible to obtain both the first illumination image andthe second illumination image in a single imaging operation, thusimproving the frame rate of the separated images.

In the above-described aspect, the distance D between the first exitface and the second exit face and the distance L from the first exitface and the second exit face to the subject may satisfy Expression (1)below:D/L<0.068  (1).

Due to the difference in position between the first exit face, throughwhich the first illumination light is emitted, and the second exit face,through which the second illumination light is emitted, the position ofthe specular light in the first illumination image and the position ofthe specular light in the second illumination image differ, and, in theseparated images formed from such first and second illumination images,white or black spot-like noise is generated. By satisfying Expression(1) above, the position of the specular light in the first illuminationimage and the position of the specular light in the second illuminationimage substantially coincide, thus preventing noise in the separatedimages.

In the above-described aspect, the separation processing unit mayseparate three or more sets of image information from two or more firstillumination images imaged by radiating the first illumination lighthaving dark portions with various widths, and the separated-imagegenerating unit may generate three or more separated images using thethree or more sets of image information.

By using a plurality of first illumination images of the subjectilluminated with the first illumination light having the dark portionswith various widths, it is possible to generate three or more separatedimages containing a large amount of information at different depths.

REFERENCE SIGNS LIST

-   1 endoscope system-   2 endoscope-   3 body part-   41 first illumination unit-   42 second illumination unit-   5 intensity-distribution changing unit-   6 imaging unit-   7 image processing unit-   71 separation processing unit-   72 separated-image generating unit-   L1 first illumination light-   L2 second illumination light-   A biological tissue-   B surface-   C surface layer-   D deep layer

The invention claimed is:
 1. An endoscope system comprising: a firstlight source that is configured to emit, from a first exit face to asubject, first illumination light for imaging two sets of imageinformation about the subject at different depths; a second light sourcethat is configured to emit, from a second exit face disposed at adifferent position from the first exit face to the subject, secondillumination light having a wide band covering a visible band; and aprocessor comprising hardware, the processor being configured to:receive a first illumination image of the subject illuminated with thefirst illumination light and a second illumination image of the subjectilluminated with the second illumination light; separate the two sets ofimage information from the first illumination image; and process thesecond illumination image using the two sets of image information togenerate two separated images each containing a large amount ofinformation about the subject at the different depths; wherein the firstillumination light has a spatially non-uniform intensity distributionincluding light portions and dark portions in a beam cross-sectionperpendicular to an optical axis, a first set of the two sets of imageinformation is a deep-layer component image that contains moreinformation about a deep layer of the subject than a second set of thetwo sets, and the second set of the two sets of image information is asurface-layer component image that contains more information about asurface and a surface layer of the subject than the deep-layer componentimage, and the processor is configured to: generate a deep layer imagein which information about the deep layer of the subject is emphasizedover information about the surface and the surface layer of the subjectby using and processing the deep-layer component image and the surfacelayer component image; and generate a surface layer image in whichinformation about the surface and the surface layer of the subject isemphasized over the deep layer image by using and processing thesurface-layer component image and the deep layer component image.
 2. Theendoscope system according to claim 1, wherein the light portions andthe dark portions included in the first illumination light areband-shaped, and the light portions and the dark portions arealternately repeated in a width direction, forming a stripe shape. 3.The endoscope system according to claim 2, wherein the light portionsand the dark portions included in the first illumination light have asubstantially sine-wave-shaped intensity profile in the width direction.4. The endoscope system according to claim 2, wherein the processor isconfigured to: separate three or more sets of image information from twoor more first illumination images imaged by radiating the firstillumination light having dark portions with various widths, andgenerate three or more separated images using the three or more sets ofimage information.
 5. The endoscope system according to claim 1, whereinthe shape of the wavelength spectrum of the first illumination light isthat of a single wavelength.
 6. The endoscope system according to claim1, wherein the wavelength spectrum of the first illumination light andthe wavelength spectrum of the second illumination light have differentshapes.
 7. The endoscope system according to claim 6, wherein the firstillumination light and the second illumination light have differentwavelength bands.
 8. The endoscope system according to claim 1, whereinthe wavelength band of the first illumination light is an infrared band.9. The endoscope system according to claim 1, wherein the first lightsource and the second light source simultaneously emit the firstillumination light and the second illumination light.
 10. The endoscopesystem according to claim 1, wherein a distance D between the first exitface and the second exit face and a distance L from the first exit faceand the second exit face to the subject satisfy Expression (1) below:D/L<0.068  (1).
 11. The endoscope system according to claim 1, whereinthe processor generates the surface layer image on the basis ofExpression (a) below and generates the deep layer image on the basis ofExpression (b) below:surface-layer image=second illumination image×surface-layer componentimage/(surface-layer component image+deep-layer component image)  (a)deep-layer image=second illumination image+deep-layer componentimage/(surface-layer component image+deep-layer component image)  (b).12. The endoscope system according to claim 1, wherein the processorgenerates the surface layer image on the basis of Expression (a) belowand generates the deep layer image on the basis of Expression (b) below:surface-layer image=second illumination image×P×surface-layer componentimage/(surface-layer component image+deep-layer component image)  (a)deep-layer image=second illumination image×Q×deep-layer componentimage/(surface-layer component image+deep-layer component image)  (b)where P and Q are coefficients.